Mobile robots have gradually been deployed into our everyday lives. Entertainment robots, floor-cleaning robots, security guard robots, and others have been made commercially available. Human-type robots (humanoids) are demonstrating reliable running motion in research laboratories in Japan (for instance, a patent WO/2006/062948 discloses technology on a legged robot). Extensive attempts have been made to make those autonomous robots understand their surroundings.
Patents WO/2006/046053, WO/2006/046049, and WO/2006/046044 discuss methods of cleaning a flooring surface with a dedicated hardware system. However, they do not mention how the robot recognizes its surroundings.
Another patent WO/2005/092632 discloses a method for a mobile robot to navigate using two-dimensional barcodes which are formed at predetermined intervals on a floor. However, installing the extra-hardware on the floor is expensive and time-consuming for users.
Another patent WO/2005/098476 discloses a method for an autonomous mobile robot to estimate its position using optical emitters and optical sensors to detect their reflected light. However, the use of the light source makes the application of this robot expensive and limits its application possibilities.
Other patents WO/99/59042 and WO/2000/043186 disclose methods for a mobile robot to systematically cover an area by pasting boundary markers and by sensing the area edges. The use of special markers makes the system expensive and installation tedious, and limits its application areas.
Other patents WO/2005/081074, WO/2005/006098, and WO/1999/028800 disclose methods for a mobile robot to dock to a base station. This method helps the robot to understand the geometrical relations around the base station, but the robot's understanding of the whole operation area cannot be expected.
Another patent WO/2001/038945 discloses a method of mapping surroundings using multiple mobile robots. However, if there is a method using only one robot would be much more useful.
Another invention U.S. Pat. No. 6,009,359 describes methods of mobile mapping to generate a geometrically precise three-dimensional detailed model of an unknown indoor environment. However, how to avoid odometry errors on a mobile robot is not specifically described.
Still another invention U.S. Pat. No. 6,965,209 discloses a method for a robot to confine to a particular space by using a portable barrier signal transmitter. However, obviously, a method that does not use such a hardware piece is preferred.
Patent disclosures WO/88/004081 and U.S. Pat. No. 4,821,192, describe a mobile robot navigation method using a node map. The node map is pre-designed by a human and given to the robot as data. What advantages can be expected by using this node map in not clearly addressed.
Traditionally, the Simultaneous Localization And Mapping (SLAM) approach has been pursued in the robotics research community for the purpose of mapping an unknown operation area. In this approach, a self-contained autonomous mobile robot is supposed to explore and map unknown surroundings by itself.
A patent disclosure WO/2004/059900 describes a SLAM method using image sensors. Another patent WO/2001/078951 discloses a method for a mobile robot to find a semi-optimal path to a given goal in a wholly unknown, unpredictable and partly, dynamic large-scale environment. Another patent U.S. Pat. No. 7,015,831, describes methods of generating and updating a map with a visual sensor and the SLAM technology.
Limitations of the SLAM approach are as follows: (1) The precision of the map obtained is limited because of the mobile robot's poor odometry capability (“odometry” is the function of a mobile robot that estimates its own robot frame ((x, y), θ) by accumulating the robot's incremental movement at each sampling time). (2) The robot loses its positional identification in a complex operation area because of odometry errors, and hence, autonomous mapping of a complex operation area becomes very difficult. (3) Furthermore, this approach lacks a fundamental consideration in the mapping problem: Depending on situations, a robot may have to deal with multiple operation areas in given surroundings. The robot is never able to know these distinct operation areas autonomously without humans' instruction.
An algorithm for a mobile robot to track a linear or circular path using the curvature is disclosed in U.S. Pat. No. 6,134,486. This algorithm is useful if v≠0, and hence, the curvature is defined. However, in this present invention, the condition (v≠0) is not guaranteed. Therefore, the present invention does not adopt this prior invention.
An algorithm for recording a manually driven vehicle's motion is disclosed in a patent U.S. Pat. No. 6,314,341. In this prior patent, the robot's motion is generated by human's physical force while the motors' power is off. This motion-generation means is not useful enough in case the robot is too heavy for a human to move around.